Resonator



R. F. BEERS March 1, 1932.

RESONATOR Filed Oct. 27; 1928 INVENTOR. Kb/00a Beer-S A TTORNE Y.

'atented Maul, i932 OLAND IF. BEERS, OF BELMONT, IllliIASSACHUSE'I.'JIS, ASSIGNOR TO SUBMARINE SIGNAL COMPANY, OF BOSTON, MASSACHUSETTS, A CORPORATION OF MAINE RESONATOR Application filed October 27, 1928. Serial No. 315,500.

The present invention relates to water resoitors and in particular to such resonators ounted withina vessel or on the skin of Le same.

While resonators date from the time of felmholtz, who first explained their theory operation and showed particularly their )plication to resonance in air, very little .ogress has been made in applying them for :e in under water signaling. Attempts have zen made, as shown in the Burgess et al. atents 1,301,034 and 1,301,035. to use water sonators, but apparently the resonator self was taken forgranted and no thought .ven to the type or kind needed for success-- ll operation. In fact, up to the time of the resent invention, it has been considered imissible to design a resonator which would be tactical and useful in operation in a water edium. The general view is expressed in Le German book by Franz Aigner, Unterasserschalltechnik, page 79, the last para- .aph in particular, in which the author ates, after pointing out that water is 3500 mes as sound hard as air:

To this conclusion we wish to add still anher important remark for practical consid *ation. There has not been a lack of atmpts in submarine acoustics to construct ater resonators similar to-air resonators. he former, on account of the great water lrdness, must be provided with an unusualthick wall to attain the same stiffness in .e medium as compared to air. This is so flicult to attain, however, that the reso- H108 effect will be very much poorer than in r if very special care is not taken.- If, how- 'er, the great sound hardness of the water taken into account, exceptionally heavy ructures result which -cannotat'all .be built a ship. For these same reasons water histles, the walls of which had to have simir protective thicknesses and weights, have chance of success. I The relation between the thickness and dineter of a cylinder to be harder or as hard where K is the compressibility and E the modulus of elasticity. For steel, the author gives this as i i. D 100 Consideration, however, will show that the relation of thickness to diameter of the value of 1/100 is really not very difficult to obtain and that under ordinary conditions this ratio will be even greater. Ordinary construction to provide walls thick enough to Withwhich, to all physical appearances, gave the investigators the'belief that the difiiculty was that of obtaining a resonator of sufiicient stiffness.

The difficulty in the past has been that no potential sound energy could be stored up in thediaphragm because apparently the pressure within the resonator could not be built up on account of the expanding of the" walls were not stiif or rigid to the forces set up. I This phenomenon was shown to be experimentally true by comparison of a resonator p which was absolutely air free with one 1n I,"-

which a given amount of air was introduced. In the latter, noappreciable pressure'could be built up'and the resonator not only was far off frequency but very ineflicient. Changing the amount of air in the resonator changed both the efficiency and frequency, and in fact any one condition was found hard to duplicate.

In the construction of the resonator I have also found that with equal and perhaps better efiiciency and operation a smaller reso nator was more desirable than a large one, and I have thereby been able to provide a resonator giving excellent results which can be mounted on the skin of a vessel exposed to the sound transmitting medium where formerly this was impractical on account of the. bulk and weight which so affected the surrounding ships plates that the sound energy was diverted from the resonator. The Weight of the resonator lowered the nat ural frequency of the plates so that a pres sure release was provided right in the vicinity of the resonator and no pressure amplitude could be built up.

Besides the features above mentioned, the construction itself provides some new features not practicedin the prior art. These will be learned from the description and drawings, in which Figure 1 shows a sectional view of one form of the invention,

Figure 2 shows a sectional view of a modification, and

Figure 3 shows a sectional view of a further modification.

' In Figure 1, the resonator 2 is mounted on the skin 1 of the vessel 1, in the same manner that a water tank used for receiving sound is mounted. In this modification the device is provided with an outer tank 4 connecting with the resonator proper by a passage or orifice 14. The outer tank 4 is formed as an integral part of the whole device and is rovided with aheav g flange 20 having em edded therein a rub er ring 6 which acts not only to keep the water within the tank from leaking out but also as a sound insulator. The resonator 2 has in its upper part the resonator chamber 3 which is surrounded by a heavy cylindrical wall, having at its upper part a heavy flange 7 to which the back plate 8 is firmly fastened by bolts 15 or other suitable means. The plate 8 is provided with an opening 12 in'which is inserted a diaphragm 9 carrying the microphone 10. The microphone is enclosed preferably in an air tight casing 5 to protect it from physical damage. The casing 5 is provided with a cable head 13 through which the electric cable 11 passes carrying leads to the microphone 10. At the topmost part of the resonator chamber 3 is p povided a hole 27 which does not appear in 'gure 1, since the view is a horizontal section. This is shown in Figure 3, and may also serve as a means',for filllng the resonator with water as well as for drivin out the air adhering to the sides and top of t e resonator chamber itself. The air may be driven out in any suitable wag, as by rap in the sides of the chamber an the top or By oiling the water contained therein in the resonator either before or after it is filled.

In the modification shown in Figure 2, the resonator is mounted directly in the skin having its openin or orifice 14 directly to the outer water. this modification, which is preferable in many respects to the others, the resonator is really in direct communication with the outer water, except for a thin shell or blister 25 partially shielding the space 24. The blister may be made of metal, for example, steel, or other sound transmitting material. As indicated,'the wall of the blister 25 is very thin and constructed so that the sound waves are very little hindered by it. In fact, the blister 25 does not need to be water tight but can be put on in such a way that the water can enter slowly from the outer water medium. One of the chief advantages of this construction is that the water rushln by the blister when the ship is in motion oes not produce a resonant note in the resonator, as is quite often the case when a fluid rushes by an orifice or opening. A similar effect would occur if one blew across the top of a bottle.

The resonator in Figure 2 is separated from the skin'l by means of a heavy rubber insulating washer 26 which fits over the shoulder and neck of the resonator and into the opening in the vessel. In other respects the modification shown in Figure 2 is similar to that of Figure 1.

In Figure 3, the resonator is mounted in a tank 16 of the usual receiving tank type except that it is provided at one corner with a supporting member 17 to which the resonator 2 is firmly fastened. The resonator itself is similar to that of Figure 2. The sound, however, instead of entering from the outer water directly to the resonator, as is the case in Figure 2, first passes through the tank chamber and then into the resonator.

As has been mentioned before, in the topmost part of the resonator chamber a hole 27 is provided which can be plugged up by the plug 29 after the air has been driven out. In fact, the hole 27 can be omitted if the air is driven out of the resonator chamber through the orifice 14 by boiling or otherwise. This may be accomplished before installation by holding the resonator chamber in such a position that the orifice is the topmost part of the same, filling it then with water and driving the air out by shaking, rapping or boiling. After the air is out the orifice may be plugged uptemporarily until the resonator is put in its position and the tank filled with water. after which the plug may be removed. In Figure 3, a hole 30 is provided in the top 01 the tank throughv which the tank can befilled and in which the hand may be inserted to pull a plug-which maybe puti'in the orifice. 14.

Besides taking these precautions to prevent air from remaining in the resonator, I have found also that when the resonator chamber is a casting, the castin is apt to be somewhat porous and have sma l cavities from which it is hard to dislodge the air. may be overcome by coating the inside with enamel 28 or cement and thereby, filling up these cavities.

In the illustration shown in Figure 1, the chamber 4 provides a means for increasing the sound pressure at the orifice 14 by couplin with the skin in such a manner that the amp itude of motion from the skin to the orifice is multiplied for the frequency of resonance. The chamber in this-instance is equivalent to a so. called fton-pilz or an elastic member comprisingthe elasticity of the water mass and two masses connected thereby, comprising the orifice mass and its fvatier load and the skin mass and its water The word ton-pilz is of German origin and is commonly understood to mean two masses connected by a substantially massless elastic member, the whole forming a vibratory system having a particular resonant frequency.

In the construction shown in Figure 1, the combination of this arrangement with the resonator is particularly useful, since it not only provides a very good tunifig .not too broad and not too sharp on account of the coupling, and also a very efiicient receiving element, since thesound energy at the orifice of the resonator is in a very much better form to be handled, it being already concentrated in the manner in which the resonator'is best able to handle it.

In. my construction I am able to operate resonators efiiciently and with all the practical reliability necessary for any commercial construction. I have obtained amplification twice as great or'more than twice as great as the best receiving apparatus heretofore used has ever given, and in addition perhaps even more useful, have eliminated all water noise and noise of signals other than those of the desired frequency.

Having now described my invention, 1 claim: l r 1. A submarine acoustic apparatus comprising a water resonator free from air.

2. A sound receiving apparatus comprising a water resonator, a hydrophone and means for coupling mechanically and acoustically said hydrophone to said resonator,

said resonator chamber being air free.

3. A sound receiving apparatus compris- This difiiculty' 4. In combination, a vessel and a sound receiving apparatus mounted on the skin thereof, including an opening provided in said skin, a resonator having its orifice fitting in said opening and a thin shell enclos ing a large dead water space surrounding said opening.

6. In combination, a vessel and a sound receiving apparatus mounted on the skin thereof including a liquid filled resonator having an orifice and a chamber communicating with said resonator, said chamber being filled with liquid and abutting the skin of the vessel.

7. In combination, a vessel and a sound receiving apparatus mounted on the skin thereof including an orifice anda second chamber communicating to said resonator through said orifice, said second chamber being filled with liquid and abutting the skin of the vessel and forming a coupling means between the resonator and the skin for amplifying the amplitude of motion of the sound wave received at the skin at the resonator orifice.

8. In combination, a vessel and a sound receiving apparatus mounted on the skin thereof including a casing provided with two chambers, an opening connecting said cham-' bers, a hydrophone positioned in one of said chambers, said chamber being resonant to the frequency to be received.

9. In combination, a vessel and a sound re ceiving apparatus mounted on the skin thereof including a casing provided with two chambers, an opening connecting said chambers, a hydrophone positioned in one of said chambers, said chamber being resonant to the frequency to be received and said other chamber being adapted to amplify the amplitude of motion of the sound wave received at the skin at the orifice of the resonator.

10. A submarine acoustic apparatus comprising sound receiving means, a resonating chamber associated therewith filled with water free from air, the system being resonant to the frequency of the sound to be received. In testimony whereof I aflix my signature.

, ROLAND F. BEERS.

ing a water resonator, a hydrophone and means for coupling mechanically and-acoustically said hydrophone to said resonator,

said resonator chamber being provided with an air vent at its topmost part to enable the air intheresonator to escape. 

